1. Field
The present invention relates to a gas shower, as well as to a lithographic apparatus and a use of a gas shower.
2. Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The application of gas showers is known from the art. For example, European patent EP 0 498 499 illustrates, in a FIG. 18, part of a lithographic apparatus. The apparatus includes a interferometer system and a space in which respective interferometer beams propagate. A constant, preferably laminar stream of air is passed through this space, to obtain a greater accuracy of the interferometer system. Both the purity and the temperature of the supplied air can be controlled. The air is, for example, of purity class 1 and its temperature is, for example, stable within 0.1° C.
U.S. Pat. No. 6,522,385 B2 discloses a different air shower. This air shower, which is disposed between a wafer stage and a lens, comprises a circular head having an upper frame and a porous member bottom attached to the bottom of the upper frame. The thickness of the air shower head increases radially outwardly from a center hole of the head. The head is being used to shower the wafer stage of a lithographic apparatus to prevent contamination of the wafer stage.